In the field of rotary printing machines, it is generally well known to provide an inking unit that is equipped with a chamber doctor blade assembly. Such a chamber doctor blade assembly will include an elongated doctor blade chamber which is provided with a central, ink receiving reservoir. The doctor blade chamber central ink receiving reservoir is defined by two spaced doctor blades which extend in the axial direction of a cooperating ink roller, typically an anilox or screen roller. End plates are used at both ends of the doctor blade body to define, in cooperation with the two spaced doctor blades, the ink receiving reservoir.
Ink is supplied to the reservoir in the doctor blade body and is then applied to the surface of the anilox roller from that reservoir while the surface of the anilox roller or other similar inking roller passes through the ink reservoir defined by the two doctor blades and end plates. It is necessary that the ink being applied to the surface of the anilox roller be accurately and uniformly metered. Either too little ink, too much ink or an unequal ink thickness along the axial length of the anilox roller will cause degradation of the quality of the resultant printed product.
The force with which the two spaced doctor blades are engaged against the surface of the anilox roller is one way to meter the thickness of the ink layer which is applied to the surface of the anilox roller. While factors such as ink viscosity, roller rotational speed and the like will also affect the ink thickness, it is the force with which the doctor blades engage the pocketed or cell-covered surface of the anilox roller which is more determinative of the thickness of the ink layer which is applied from the ink reservoir in the doctor blade chamber to the anilox roller.
In early doctor blade systems, which were used with only single or double width printing cylinders, the structure of the doctor blade chamber could be of metal since weight was not a great consideration. The use of metal doctor blade chambers imparted a certain amount of structural rigidity to the doctor blade chamber. Biasing forces could be exerted on the chamber at the ends and would be applied relatively uniformly along the entire lengths of the working and closing doctor blades.
Printing presses now in use are characterized by four wide and six wide printing cylinders. The width of such a cylinder is thus four or six times the width of a newspaper page in broadsheet format. The width of the anilox inking roller thus is typically as great as the width of the printing cylinder. This results in the need for a doctor blade chamber that also has the width of up to six newspaper pages in broadsheet format. A traditional metal doctor blade chamber becomes too heavy to be usable.
The end seals and the doctor blades of the doctor blade chamber themselves are wear items which periodically must be replaced or refurbished. It is also necessary to periodically remove the doctor blade chamber from its associated mounting assemblies so that it can be cleaned or replaced. The doctor blade assemblies are also periodically thrown off or moved out of contact with the anilox roller so that the roller can be removed from the printing press. All of these requirements of the doctor blade chamber also mean that the weight of the doctor blade chamber needs to be kept at a minimum.
One material which has shown itself to be particularly suited for use in the formation of doctor blade chambers is glass fiber reinforced plastic or GRP. Such a material is light in weight and is extremely resistant to chemicals having extreme pH levels. Many currently used printing inks have such high pH levels. While an aluminum or an iron material can be imbued with similar resistance properties, this can be accomplished only through the use of costly and complicated coatings. Such coating are always subject to mechanical damage, such as chipping and scratching. The so-coated aluminum or iron doctor blade chambers are still very heavy and are thus difficult to mount, dismount and handle.
GRP doctor blade chamber structures satisfy the need for being light in weight, having durability and being resistant to high pH levels. Their primary limitation is a lack of structural rigidity, when compared with the previously used metal doctor blade chambers. The lack of structural rigidity results in twisting and bending of the doctor blade chamber across the width of the anilox roller. If the chamber flexes, distorts or bends, the two doctor blades do not contact the anilox roller with uniform pressure along the width of the anilox roller. The result of such non-uniform contact force is variance in the ink thickness application to the anilox roller, uneven wear of the doctor blades, premature end seal failures and other undesirable consequences.
In an effort to counteract or to compensate for the lack of structural rigidity of the GRP doctor blade chambers, as compared to the prior metal structures, various attempts have been made to rigidify such GRP doctor blade chambers. One prior attempt to overcome this lack of structural rigidity of GRP doctor blade chambers is set forth in EP 1 398 152 A1. In the system disclosed in that document, the doctor blade body is provided with elongated stiffening traction elements that extend parallel to the axis of the anilox roller, in the body of the doctor blade. These traction elements extend beyond the ends of the doctor blade body and are supported by. adjustment sleeves. Those sleeves are secured onto the ends of the traction elements and are actuated to impart a flexural movement to the doctor blade body that is asserted to be substantially equal and opposite to the flexural movement generated on the doctor blade body during the inking of the anilox roller.
Another arrangement, as proposed by KBA-Motter, uses a GRP chamber doctor blade that is mounted onto a shaft via plates which are welded to the shaft. That shaft is supported, at its outbound ends by pneumatic or hydraulic cylinders. The force required to adjust the doctor blade chamber is applied by these two cylinders. This is apt to result in a transverse deflection of the supporting shaft and of the doctor blade chamber. As discussed above, such a deflection results in distortion of the GRP doctor blade chamber, a twisting of the blade system and premature wear of the end seals. Another limitation of this prior system is that the working doctor blade is located closer to the axis of rotation of the anilox roller than is the closing doctor blade. The working doctor blade is thus subjected to greater wear and tear than is the closing doctor blade. As a result, more frequent maintenance is apt to be required.
It will be apparent that a need exists for a doctor blade system which overcomes the limitations of the prior device. The doctor blade system, in accordance with the present invention, provides such an assembly and system. It is a substantial improvement over the prior systems.